Perception of bronchoconstriction in smokers with airflow limitation

To our knowledge, no data have been provided as to whether and to what exte nt dynamic hyperinflation, through its deleterious effect on inspiratory mu scle function, affects the perception of dyspnoea during induced bronchocon striction in patients with chronic airflow obstruction. We hypothesized tha t dynamic hyperinflation accounts in part for the variability in dyspnoea d uring acute bronchoconstriction. We therefore studied 39 consecutive clinic ally stable patients whose pulmonary function data were as follows (% of pr edicted value): vital capacity (VC), 97.8% (S.D. 16.0%); functional residua l capacity, 105.0% (18.8%); actual forced expiratory volume in I s (FEVI)/V C ratio, 56.1% (6.3%). Perception of dyspnoea using the Borg scale was asse ssed during a methacholine-induced fall in FEVI. The clinical score and the treatment score, the level of bronchial hyper-responsiveness and the cytol ogical sputum differential count were also assessed. In each patient, the p ercentage fall in FEV, and the concurrent Borg rating were linearly related , with the mean slope (PD slope) being 0.09 (0.06). The percentage fall in FEVI accounted for between 41% and 94% of the variation in the Borg score. At a 20% fall in FEVI, the decrease in inspiratory capacity (AIC) was 0.156 (0.050) litres. Patients were divided into three subgroups according to th e PD slope (arbitrary units/% fall in FEVI): subgroup I [eight hypoperceive rs; PD slope 0.026 (0.005)], subgroup II [26 moderate perceivers; 0.090 (0. 037)] and subgroup III [five hyperperceivers; 0.200 (0.044)]. By applying s tepwise multiple regression analysis with the PD slope as the dependent var iable; and other characteristics (demographic, clinical and functional char acteristics, smoking history, level of bronchial hyper-responsiveness and s putum cytological profile) as independent variables, AIC (r(2) = 45%, P < 0 .00001) and to a lesser extent treatment score (r(2) = 17.3%, P < 0.0006), and to an even lesser extent age (r(2) = 3%, P < 0.05), independently predi cted a substantial amount (r(2) = 65.27%, P < 0.00001) of the variability i n the Borg slope. Thus acute hyperinflation, and to a lesser extent treatme nt score and age, account in part for the variability in the perception of dyspnoea after accounting for changes in FEVI during bronchoconstriction in patients with chronic airflow obstruction.